Aspects of reproduction in acarines of public health importance are being investigated. Dermacentor variabilis receives primary attention, but other species of ixodid and argasid ticks and mites are studied to various degrees. Investigations involve (1) histological, SEM, labeling and autoradiography analyses of growth and differentiation of reproductive systems, (2) studies of spermatogenesis, spermiogenesis and sperm capacitation, (3) factors responsible for egg maturation and oviposition, (4) effects of hormones on development and reproduction, and (5) study of aggregation, sex attraction and reproductive biology of Dermanyssus gallinae. Our results will contribute to basic understanding of reproduction and development in parasitic arthropods and help make possible larger generalizations regarding arthropod and other animal reproduction. Specific data on reproduction in acarines should allow better utilization of current control schemes and hopefully provide the data base from which improved pest control schemes might be derived.